Process of drying materials



Jan. 5 1926.

M. D. .JoNlEs PROCESS oF DRYING MATERIALS Filed March 18 1924 s sheets-.sheet 1 Jan. 5 1926. 1,568,738

M. D. JONES n PROCESS OF DRYIG MATERIALS V Filed March 18. 1924 3 Sheets-Sheet 2 Patented Jan. 5, 1926.

tJNlTED STATI-:siii

PATENT oFFICE.

` MICHAEL DOLAND JONES, OF ALLENTO-WN, PENNSYLVANIA, ASSIGNOR TO FULLER FUEL COMPANY, A CORPORATION 0F PENNSYLVANIA.

PROCESS F DRYING MATERIALS.

applicati@ mea Maren is, 1924. serieu no. 700,174.

To all whom t may concern."

Be it known that I, M1cHAnL'-DoLAND JoNns, a citizenof theUnited States', and a resident of Allentown, in the county of Le- 5 high and State of Pennsylvania, have invented a new and useful Process of Drying Materials, of which the following is a full, clear, and exact description'.

This invention relates to a process for dry- 'ing materials, which is of especial `advantage for drying substances of a combustible character, such as fuels, by the'utilization of the sensible heatv of gases of combustion .from other processes. -More particularly,

this improved process is intended to be employed in the drying of coal which ls-to be pulverized and burnedl in the pulverulent condition, the Waste gases` from the furnace providing the necessary heat for the drying operation. `The following description relating to this adaptation of the process is to be understood as illustrative merely of one typical use of thek process, which iscapable of general utility. g

' Attempts have been made heretofore to operate processes for combustible materials in which waste gaseous products ofv combustion from other processes havebeen used as' thesource of heat, but these attempts have not been wholly successful.V On the contrary, it has been found that the material to be dried frequently ignites in certain parts of thedrier, while'in other parts, the moisture content, instead of being diminf ished, is actually increased. Even if igni tion does not take lace, the material discharged from the drler is variable as to dryness, and may be said to be streaked with moisture. When such material is coal which is to be pulverized, the presence of this moisture causes serious ,diiiculties in the pu vverizing operation.

In vertical driers, through which the material passes by gravity, it is often found a heating medium results frequently in a transfer of heat to the material at one side of the drier, rapidly raising its temperature o side of the drier, a transfer of moisture to the material occurs, thus increasing its moisture content. In rotary driers, operated with the same heating medium, thls con- `that the gse of waste gases'of combustion, as

to the pointof ignition, while in the other' densation of moisture takes place at the lower end of the drier and the moistureladen gases passing along the drier prevent successful operation. At present, such installations usually include a primary source of heat, either for the drier or the gases to be passed through it, and this is evidently va wasteful and expensive adjunct.

I have found that these unsatisfactory results, following utilization of waste gases for drying purposes, are brought about by f ailure to carry on the process .under condit1ons which cause a proper balance of vapor tensions within the drying chamber', and because this factor is neglected, it is only by the merest chance that the use of waste gases is accompanied by any degree of success. According tomy invention', however, I employ waste gases of combustion for the drya ing medium, which are normally of relatively .high sensible heat and of high water vapor or steam content, but with these gases I mix another gas, such as air, of a lower moisture content. The mixture of these gases is brought about under such regulation that a portion of the 'sensible heat of the wastev gases is utilized to increase the temperature of the second gas, and the resultmg mixture is one which has a relatively low moisture content. This mixture, at the desired temperature, is passed through the materials to be dried andit causes an evaporation of the entrainedmoistu're therein un- 'are combustible. Such waste gases normally' contain moisture at such vapor tension and the sensible heat is such that the heatl units in the dried, but, on the contrary, only serve raise the temperature of the latter untll igmes cannot be used for evaporatingl Vthe mo1sture content of the materials tobe tion occurs. Also, under certain conditlons l the vapor tension of the entrained moisture inthe combustible materials may be s uch that the temperature of the gaseous medlunl falls to the point that moisture therefrom 1s deposited in the materials, thus wettxmg these materials instead of drvinnr them'.

ucts below the ignition point of the combustible to be dried, prior to the admission of these products to the drier. According to the proposed method, no attempt is made to regulate the mixing operation to secure a gaseous product of suitable moisture content,

so that the sensible heat of the product canl be used for evaporating the entrained moisture inthe materials to be dried. This failure to recognize the para-mount importance of the regula-tion of the quantity of moisture present in the drying medium has made the proposed method unsatisfactory, because, as will be presently pointed out, it is the balance of vapor tensions in the drying chamber, which is the controlling factor in successful drying, and not temperature. Since, in the proposed method. the temperature only of the drying medium is regulated, and no attempt is made to secure a medium of proper moisturecontent, it is only by accident that the proper conditions for drying are set up in the chamber.

The present invention is based on the application of certain physical laws, relating,r to the action of gases containing varying quantities of water vapor, and a briet` discussion of these laws will serve to make clear the manner in which the present process is carried on.

Water vapor cannot exist. under standard conditions. but condenses to liquid at 212 F., if under 760 millimeters of mercury pressure. AIt exists at lower temperatures than 212 F., but only under partial pressures of fractions of an atmosphere. At a pressure of 1/15 of an atmosphere, when it forms 1/15 of a mixture of gases, it cannot exist uncondensed at a temperature of 100 F.

It is known that, on converting water into steam or vapor under a constant tension of 760 m. m., of mercury, it is necessary to maintain a corresponding temperature of 212 F. at which temperaure the water will be evaporated, and the more B. t. u. supplied the greater the rate of evaporation without increase of temperature.

Should the tension of the water be reduced below'760 m. m. of mercury, the temperature at which the water will be evaporated will reduce accordingly, and the more B. t. u. ,Supplied the greatel the rate of evaporation wihout raising the temperature of the water. In eliminating the moisture from combustible materials, I have taken advantage of these conditions.

I have also taken into consideration in my invention. that moisture is usually retained in materials at a tension far below 7 60 m. m.

of mercury, and, during the process of evaporation, while the tension remains constant, the temperature remains constant, and an increase in the number of heat units supplied only tends to'increase the rate of evaporation of the moisture and does not raise the temperature of the moisture or the material containing the moisture.

When gases which contain moisture under a certain vapor tension pass through material in a drier, which contains moisture under a less tension, then moisture Hows from the gas into the material, but if the tension conditions are reversed, moisture will flow fromA the material to the gas. In the first case. the processV is one of condensation, and a liberation of heat occurs at the surface of the solid materials, tending to raise the temperature thereof, while, in the second case, the process is one of evaporation, and the heat of the gases is used for useful work.

According to the methods of the prior art der 71 m. m. of mercury, these gases will evaporate moisture only in those portions of the material to be Vdried where the gases are sufficiently high in temperature as to retain moisture in suspension` but as the gases flow through the material, their temperature falls, and eventually reaches a point where moisture is redeposited in these materials. Thus, in that part of the drier where evaporation has taken place, the sensible heat of the gases then serves to raise the tempera; Ature of the solid material and, in the case of combustibles. this may eventually reach the ignition point. According to this old method, in order to eliminate moisture, the vtemperature of the entire mass of the material has to be raised to a temperature which is` dangerous when the material to be dried is combustible.

Furthermore, if the drier be operated ac cording to the prior methods so as to main- .tain a constant temperature in the materials being dried, as, for example, 100 F., and if the waste gases entering the drier have a moisture content under a. tension of 71 m. m. of mercury, with the-tension of the moisture in the materials to be dried at 50 m. m. of mercury, then it is found that after the material has passed through the drier it contains .7359-.5=.2359 lbs. more moisture than when it entered, for every 12.15 lbs. of waste gases passing through the drier. The earlier attempts, therefore, to use waste gases for drying were unsuccessful, as under the conditions of operation moisture was often added to the materials to be dried instead of being abstracted from them.

In order to make'the practice of this invention clear, the following example of the operation of a drier according to my process llascars@ willbe given, these calculations being based on actual operating conditions, although it l,as a heating medium waste gases of combustion fromanother furnace, a heating urnace, or the like. As-f rocess, such as a boiler suming that the waste gases contain moistu're-'undera tension of 71 m. m. of mercury, then to eliminate moisture from a combustible material, wherein such moisture is contained under a vapor tension of 50 m. m.

of mercury, I bring about a mixture of the 'waste gases with another gas, such as air,

. which contains moisture under -a vapor tension of, for example 15 m. m.y of mercury, tlns mixture being in the pro lortion of 12.15 lbs. of waste gases to 23.25 l s. of the other gas. In this operation a certain proportion of the sensible heat of the waste gas, for exzrenple, 216B. t. u. of the sensible heat, is u to ortion of the sensible heat, for example 695 t, u. is used to evaporate the molsture 4held in .the materials tobedried at a .tension of 50' m. m. of mercury. The gases mixed -in the regulated proportions 'above given, vwill serve tomaintain a constant and uniform temperature in the lmaterials in the drier,

l and under zproperregulation an increase in the 'available sensible heat can be utilized to increase the rate of evaporation.

It willfbeapparentxfrom the above that the purpose in diluting thaw-aste gases with air or another gas is not primarily `,to reduce the temperature of the mixture,; although this .result necessarilyv follows, for.. as.1ong

as the balance l off-vapor tensions .in the ldry-- ing chamber is maintained, increasesm temperature vwill serve onlyfto accelerate the rate 'of evaporation, and will nothave the effect of transferringheatto. the combustible material. to the extent that ignition may be brought .about-fin the' latter; Furthermore,

.even though the mixture ,of air with the- .Waste gases 'wllreduce .the'temperature of the m1xture,pthen if the vapor tension balance is not maintained; that is if the 'vapor tension of themoisturecarried' by .the waster gases is .higher than the va r tension of the moisture inthe combustible material, there will still be a transfer of heat to the combustible material andthe latter may be ignited.

The vbalance in vapor tensions above out-- Ilined is exemplaryof the operation ofthe process and w11l serve 'as a basis upon' which the process cmay' be appliedl in installations in which the' factors of operation differ. The relations according to which the final mixture to be used as a drying mediumis brought about are derived as follows: 4

Assuming that the wastegaseous products 4.7 921 lbs.

for combustion of combustion which are to b'e used for drying purposes, are derived from the burning coal of the iollgwing analysis g .1088 lbs. ox gen, these quantities being derived from t e moisture present.

There'would also be .3760X24/28;.3223 lbs. carbon, and .3760X4/28=.0537 lbs. hydro en, the above amounts being derived from t e (12H4. The total hydrogen present from the coal is .0136-l-.05? 7=.0673 lbs. and the total carbon present is ,.3223+.4698= The vtotal oxygeii in the coal is .109. To unite with the hydrogen present there 1s -requlred .0673X16/2::.5384 lbs. oxygen, and to unite with or burn the carbon present, there is required '.7921X32/12=2.1123 lbs. oxygen, the total 'oxygen required for both puoses, thus being .53844-211231- 2.6507. s the coal contains .109y lbs. oxygen there is required 2.5417 lbs. oxygen to be derived from the air `admitted for lcombustion purposes. I

The total amount of water vapor or steam 'produced from eah pound of coal samounts to .0673+.5384=.6057 lbs. H2O. Also, since air contains approximately 23% by weight of oxygen, the totalugntity of airrequired w1 e r lbs. of '-a'ir, and the nitrogen present in this amount of air is 11.05-2.5417=8, 5083 lbs.

nitrogen gas. c

Upon .burning one pound of coal of the above analysis there is accordin ly produced CO2, 2,.9044 1bs.; H2O, .6057 sI aswatei. vapor or steam; N2, 8.5083 as nitrogen1 -.gas,' makmg a total of 12.0184 lbs. of' aseous products of combustion. At 629 and 15am. m. of mercury pressure, 11.05 lbs. of

air willvcarry 11,05XW54302V.

lbs. of Water vapor lso that the totaly weight of theproducts of combustion including the' moisture inthe air will amount to 12.0184+ .1302:1211486 lbs. ofgas and H2O vapor.

The total amount of water vapor or steam i `present amounts to .6057 +.1302:.7359 lbs.. Awhile the total amount of CO2 -and'N2-2 11.4127 lbs., This amount of CO2-#N2 gas carries the .7359 lbs. of water vapor which isaderived i-n part from the air for combustion and in part from the combustion of the hydrogen in the coal. At 100 F. and

50 m. m. of mercury pressure, however, 11.4127 lbs. of CO2 and N2 gas will not carry over .5 lbs. of water vapor, so that under these conditions .2359 lbs. of water will be condensed in the drier for every 12.1486 lbs. of the waste gases that enter it.

If the temperature of the 12.15 lbs. of Vgases entering the drier be 400 F. and a temperature of 100 F. is to be maintained in the materials in the drier, then a temperature drop of 300 F.takes place, and assuming the specific heat of the gases to be .25 B. t. u. per lb. there are available 12.15 .25X300:911 B. t. u. in sensible heat for every pound of coal burned and delivering waste gases. To eliminate one pound of Let t2: the temperature of the yresulting mixture.

Assuming then that the waste gases are at a temperature of 400 F. and the mean specific heat of the mixture is .25 B. t. u. per lb. 12.1486 .25 (4o0-,)=X .25(1:,62) Solving for t, and X it is found that moisture from the material in the drier will require approximately 1400 B. t. u. so that the 911 B. t. u. available will eliminate about .65 of a pound of moisture.

As the waste gases will add .2359 lbs. of water at 100 F. to the materials to be dried, then .2359)(14002330 B. t. u. are utilized to evaporate this moisture and the difference 91l-330=581 B. t. u. are available to raise the temperature of the materials in the drier.

In order to bring about the desired drying according to my process, the following equations are to be solved:

Let Xzlbs. of gas at 62 F. to be mixed with 12.15 lbs. of waste gases of combustion which at 15 m. m. of mercury will contain ==.01178 lbs. moisture per pound 'of gas.

a result of the mixlllg operation will be 11.4127 (COVE-N2) -I- +.7359-l-.01178X= l2.1486+1.01178X-t0tal Weight 0f mixed gases and vapor.

One pound of the mixed gas at 100 F. will carry about`.0438 lbs. of watervapor, or (11.412741) .0438=.5+.0438X total lbs. water vapor carried by the mixed gases, recalling that at 100 F. and 40 m. m. of mercury 11.4127 lbs. CO'2 and N, will not carry more than .5 lbs. of water vapor.

Then as the mixture of gases will carry .5+.0438X lbs; of water vapor and there are present .7359 lbs. of wat/er vapor in the waste gases, and .0117 8X lbs. of water vapor in the diluting as, the difference- (.5-1-.0438X) .7359+.01178X) .03202X4-.2359 lbs. of moisture will be eliminated from the material in the drier duringlthe passage of the mixed gases therethroug f The heat available for evaporating moisture at a constant temperature of 100 F. and at a vapor tension of 50 m. m. will be (12.1486 -l- 1.01178X) X .25

The heat required to evaporate (.03202X .2359) lbs. of moisture will be-Y Solvinr for` X, X=23.25, or for every 12.14861 s. of as and water vapor from the gaseous pr ucts of combustion, there must be addedI 23.25 lbs. of gas at 62 F.

and 15 m. m. in order to maintain a constant temperature in the materials to be dried, together with the limitation of moisture therefrom.

Solving for t2 it isfound that t2=178, the temperature of the gases entering the drier.

Then -as 23.25 lbs. of the diluting gas at 15m. m. and 62 F. contains 23.25 .01178= .2738 app?. lbs. of moisture, Aand there is present 359 water vapor in the waste gases, it follows that there are present in the materials therein. To eliminate this amount of moisture will limitedto the use o 3 heating medium, since the hot gases may be p 'supplied directly from a furnace designed 40. or several driers ma mixture 11.4127-F23.25=34.6627 lbs. of s lbs. of gas will carry 1.5062 lbs. of moisture, so that during the passage of the mixture through the drier 1.5062-1.0O97=.4.965`

lbs. of moisture will be eliminated from the require .4965X1400=695-B.`t. u. and the heat available is 35.6724)(.25 (178-100): 695 B.lt.,u. available. 1 As we have previously seen, with a temperature drop of 3009 inthe waste gases of combustion 911 B. t. u. are available-, so that 911-695 B. t. u.=216 B. t. u. are available for raising the temperature of the dilut ing gas. l o v It ,will be apparent from the foregoing description of the -process and theexample of the calculations by which the regulation of vapor tensions in the drier'is roug'ht about, that combustible materials can be *5 dried solely by waste gases in an economical and safe manner, provided the proper conditions are maintained in the drier. It will also be clear that this process is by no means waste products as a ely for that purpose, yor from an other source. For purposes of economy; l oth in operationv and construction, the use of gases o combustion from other processes, which have heretoforel been allowed to go to waste,

ispreferred. It is also evident that this process is by no means limitedjin ap licationl to any specific form of drier, an one be operated at the same time. The num r of driers will de-` pend' on the ca acity required, and also on the volumean temperature of the waste 'gases available.

In the accompanying drawings, there is illustrated one ty ical installation in which this process may e carried on, and in these drawings,- v

\ Figfl is a -diagrammaticview partly in M section showing one form of apparatus or system for carrying out my process.

Fig. 2 is aplan view of the assembly` shown in Fig. 1.

Fig. 3 is enlarged, sectional, detail view u of the air mixing device and its related apv, paratus.

f Fig. 4 is a sectional plan view taken at line vA--A of Fig. 3. l

Fig. 5 is a transverse sectional view taken Fig. 6 is an inverted plan viewl of the air mixin device looking upwardly through the air-va ve openings.

Fig. 7 is a cross-sectional viewof a detail ofthe air inlet and controlling valve.

is a smaller chamber bounded Fig. is .a longitudinalv section of the air-l I valve showing the regulating and. indicating means.

Referring particularly to'Figs. 1 and 2, a

boiler furnace, 10, is shown by way of illustration as a means for carrying out a primary process, the waste gaseous products of y which may be utilized for carrying out my process with economy. A I

A mixture of pulverized ueland primary air is admitted to the furnace through burners 11, positioned' in the front'wall 12. Secondary combustion air is admitted through .suitable dampers, such as those in the cleanout doors 13, 14.

Combustion is completed within the chamber 15 and the hot, gaseous products of combustion are drawnthrough the boiler and around the bailles as clearl indicated by the path of the arrows. en the have reached the out-let flue 17, they ave cooled considerably and contain a quantity is shown at 19 and serves toy divert any or all S of the waste gases into la liuc 20, having normally the same cross-sectional area as the stack-flue. v

A mixing device for the hot waste gases, in this instance air, is shown on an enlargedy scale in Fig. 3 and is indicated generally at 21', but it is to be understoo that any suitable air and'lue-gas mixing device may be substituted for this purpose. Y

The waste gases entering the mixing device ass downwardly past a baie 22 andr are ivided by a second deectingfbale 23. which directs a portion .of the gas horizontally, the remainder of the gases passing beyond the baffle. 23 and arel deliected by thecurved wall 24 of the mixing chamber. A plurality of V shaped, perpendicular inembers 25 serve to direct the h ot vasesinto the central vchamber 26 in par el, vertical paths.

I Air is admitted to the chamber 26 through an air-valve 27, shown in detail in Figs. 7 and 8. p o

Depending from the mixin chamber 26 gby side walls 28, 29, to which walls is secured a b `ittom plate 30, which is provided with a lurality of slots or openings 31, through w ich enterin air is admitted and controlled by a mova le plate ,32 which forms the com lementary memb'er of'the inlet valve. e plate 32 Ais provided with a pluralityof slots 33, whic slots are in sta gered relation to and half the width of t the lower plate 80.

lie

e slots 31 in A,

va sha Posts 34, secured to the plate 32 are adapted to slide in tubularl members 35 which serve as guides for the vertical movement of the upper plate.

Suiibly supported in bearings 36, 37 is 38, to which is secured centrall a cam 39. Two pillars, 40, 41 connecte at the top by a cross member 42 are secured to the movable late, the cross member 42 resting upon and) cooperating with the cam 39. An abutment plate 43 is secured to the movable plate 32 and cooperates with the cam 39 to insure downward movement of the plate if the latter fails to fall by gravity,

handle 46 passes through an aperture inv the index and serves as a means to rotate the index 44 and the shaft 38. .The inner end of the handle 46 is reduced as as 47 and engages, as a detent, one of a plurality of apertures 48 formed in the scale 45, to

lock the cam shaft 38 in any`desired position.

With particular reference to Fig.' 8, it will be observed that when the index and shaft ,the hot 38 are in the left, lowermost position, the movable plate 32 is forced against the xed plate 30, preventing the admission of air. Rotation of the shaft to the opposite position moves the late 32 to provide a maximum openin t e s 'ace between the plates being one-ha `f of t e widthl of the openings 33 or one-quarter the width of the openings 31, thus insuring an even distribution of entering air, the amount of which may be regulated accurately.

s shown in Fig.. 7,- a plurality of horizontally disposed, V shaped members 50, similar in construction and function tothe members 25, serve to direct the air upwardly in parallel staggered re ation to the openings between the members 25,1wher1-'ly'theentering airv is evenly distributed between the layers of hot gases.

To further insure a complete mixture of ases and air, an angularlyv posi- -tioned ba e 52, shown in Fig. 3, is provided with a central aperture 53, through which the mixed gases are directed against a second baiiie 54, and'thence diverted by the latter and other baiiles 55 and 56. The separation between the bailies and the openings through them are so balanced that the mixed gases are equally dividedduring their passage to insure complete mixture. The gaseous mixture is drawn through the mixing device through a ilue 57 by means of a suitable fan 58 vwhich discharges into a Hue 59. The fan further serves to complete the mixture of the two lgases.

aths through openings 51 in The flue 59 terminates in a drier indicated f at ,60 and the mixed gases are there forced through the combustible materials t0 be dried, the position of which is shown at 61 and which are allowed to fall b gravity, the dried materials being conveye from the drier by any suitable means, such as the screw conveyor 62.

The gases after having evaporated the moisture from the materials, are conveye to the atmosphere through the stack 63 by ghe natural draft and the pressure of the The operation of my process with relation to the specific apparatus shown is as follows: The temperature, moisture content, weight and volume of the flue gases passing from the flue 17 tothe stack 18 is determined or maybe estimated. The temperature and;

the materials being known, a suiicient quantity of the iuegases are diverted by means of the damper 19 into the flue 20 from which they are drawn into the air mixing device. Then, in accordance with the general statement and theory of operation of my process, as explained hereinbefore, a suiicient quantity of air is admitted through the valve 27 at the bottom of the mixin chamber 21, to provide a mixed gas heate by the flue gas and carrying moisture at a vapor tension lowered to ,a point considerably below the vapor tension of the moisture in the materials to be dried, due tothe relatively low vapor tension of the moisture carried by the air. Thedamper 19 and the index 44, which indicates the position of the air valve 27, are so positioned that, the proper mixture of gases may be obtained in accordance with .tables and equations set forth hereinbefore.

The mixed gases are drawn from the mixing device by the fan 58 and are thereby forced through the materials 61 in the drier 60, the exhaust gases being directed to the atmosphere' through thev stack 63.

It 4will'be understood from the foregoing description that my process is independent of the apparatus shown and'described, and

dvb

that other equivalent apparatus may be substitutedin whole or 'in part to carry out the same process. The relative location of the various elements may be changed, for ex- 120.

ample, the fan may be positioned on the outlet side of the drier, although it is preferred t0 employ the fan asan additional mixing device. Other air and gas mixing and controlling devices may be substituted which may be much less elaborate, and the various forms of driers substituted for the waste heat drier shown on the drawings'.

In the preferred application of my process in the arts, it is employed as a waste heat method for drying coal, as the diiculties v heretofore encountered, such as ignition and high vapor tension with other gases, and

passing the mixed` ases through the materials to be dried whi e so regulating the mixing operation as to maintain 'a uniformly.

' constant temperature in said materials.

2. The process of drying combustible materials, which comprises mixing waste gases of combustion of relatively high sensible heat and carrying moisture vat high vapor tension with other gases oi'` relatively low sensible heat and carrying moisture at low vapor tension, andpassing the mixture 'through the materials to be dried while so' re ating the mixing operation as to maintain a uniformly constant temperature in the said materials.

3. vThe process of drying combustible materials, which comprises mixing waste gases of combustion carrying moisture at highy` ,vapor tension and containing sensibleheat romthecombustion of' fuel with other gases, and passing the mixture through the materials to'be driedV while so regulating the mixing operation, that a portion, of the sensible heatof the waste gases is used toI heat the other gases and another portion of the I sensible heat is used to evaporate moisture in the materials to be dried. n

4.* The process of drying combustible material,-which comprises mixing waste ases of combustion lcarrying `moisture at igh vapor 'tension with other gases carrying.

moisture at low vapor tension, and passin the mixture through the material to be drie while regulating the mixing operation so that the mixed gases have a lower vapor tension lthan that of the. moisture in the inaterialsto be dried.v

5. The process'of dryin combustible ma' Y terial, which comprises ut' ing the sensible heat of hot gases of combustion of high moisture content to heat by mixture with a second gas `of low moisture content, and

'passin 'the mixture through the materials to be ried, the mixing operation being carried on under such conditions that the moisture-carrying capacity 'of the second-namedgas is'increased and a'portioii of the sensible heat of the irst gas is made available 'for the eva eration of themoisture in the material to e dried.

6. The process of drying combustible'mw 4.terial, which .comprises waste gas of regulating the `mixing the low vapor tension o'f the secondfgas is utilized to provide a mixedgas of comparatively lowvapor tension useful for withdrawing'moisture from the materials to be dried.l

7. The process of drying combustible mag l terials, which comprises mixing Waste gases of combustion of relatively high sensible heat and vcarrying moisture at igh vapor tension-with other gases containing moisture at low vapor tension-and of relativel low` sensible heat, and passi g the mixture through the 'materials to b dried, while so operation that a portion of the sensible eat of the first gas is utilized to heat the second gas and another portion of the sensible heat isA utilized to accelerate the drying operation.

8. The'process of drying combustible materials which comprises mixing waste gases of combustion carrying moisture at a vapor tension too high for eicient drying and of 'relatively high sensible heat, with another gas containing moisture of Arelatively low vapor tension and of relatively low sensible heat, andA passing the mixture through the materials to be dried while regulating the mixing operation to produce amixture which contains moisture at a. much lower vapor. tension than the `vapor tension ofthe moisture in the materials to be dried. v .9. The process of drying combustible materials, which comprises mix' lwaste gases of combustiony of relatively v heat and containing moisture at 'a'. relatively high vapor tension', with other gasesof relatively low sensible heat and containing moisture of relatively low vapor' tension, and passing the mixture through the materials to be dried, while controlling the mixing opigh sensible alsA eration to provide a mixture such that upon4 moisture at relatively high 'vapor'tensiom with other gases carryingmoisture at relatively low' vapor tension and so regulating and controlling the mixture that evaporation takes place, iwhen the mixed gases are passed through the materialsat a tempera- 0f inaterials which l.

ture corresponding to the vapor tension of the moisture in the to be dried.

11. The process of drying materials which consists of employing gas of relatively high sensible heat and containing moisture at relatively high vapor tension, mixing with this gas a second gas of relatively low sensible heat and containing moisture at relatively low vapor tension', regulating and controlling the mixture that evaporation takes place at a temperature corresponding to the vapor tension of the moisture inthe materials to be dried and passing the mixed gases through the materials.

12. The process of drying combustible materials which consists of so mixing and regulating gaseous products of combustion from ling the mixing of the gases so as to eva orate moisture from the materials to be dried at a temperature corresponding to the vapor tension of the moisture in the materials to be dried, whereby ignition of the materials to be dried is prevented.

In testimony whereof I aliix my signature.

MICHAEL DOLAND JONES. 

